This invention relates generally to equipment for applying resistive forces and more particularly to a specially constructed resistance pack and a resistance mechanism which provide resistance force individually and through series connected resistance packs in devices such as garage doors, cable reels, resistance exercise machines and other applications where a resilient resistive force is desired.
Springs of various types, especially steel tension springs, are used in a wide variety of applications to provide a resistive force, including resistance exercise equipment, hose and cable reels, garage doors, overhead doors and other doors, door closers, tool balancers, automotive hood and trunk balancers, various types of office and medical equipment, crowd control barriers, and a wide variety of appliances, industrial equipment, and consumer products. Steel springs are commonly used to provide resistive forces in these applications, although other devices have been used. For example, resistance exercise machines have incorporated weights, deformable resistance elements, and friction or centrifugal mechanisms to provide a resistive force. Usually, resistance exercise machines take the form of large stationary equipment. Equipment that uses weights as the resistance is obviously heavy and unsuitable for uses where light weight is essential or where portability is important.
U.S. Pat. No. 4,944,511 to Francis discloses a portable exercise machine in which resistance is provided by a variable number of stacked spring packs. Each pack has a known resistance, and the resistance packs are connected together in a manner to provide an additive force. The stacked resistance packs all rotate together so that in applications where a long extension of the cord is required, the resistance packs rotate a significant amount. When the springs approach their limit of deformation, they provide significantly increased resistance. Thus, the resistance can increase sharply during the range of motion of equipment, particularly when the cord nears a fully extended position.
Resistance elements of the type shown in U.S. Pat. No. 5,209,461 to Whightsil can be incorporated in a light weight unit which nevertheless provides considerable resistance. Therefore, this type of resistance pack has characteristics making it suitable for use in exercise equipment and other applications where light weight and portability are important. However, achieving a flat resistance-extension curve with this type of resistance pack is still difficult, particularly if the requirements include providing a large resistance force and at the same time accommodating a long extension of the cord or other actuator.
In recent years, it has been discovered that personnel stationed in a micro-gravity environment, as on a space station, tend to lose muscle mass and bone density quickly because of the absence of gravity opposing their normal movements. It is important for such personnel to have resistance exercise equipment available to allow them to exercise regularly and counteract the tendency for muscular atrophy and loss of bone density. Heavy weights are obviously not a viable option for a micro-gravity application of this type. Compactness, light weight and portability are attributes that are necessary for exercise devices intended for use on space stations and similar environments. At the same time, a large resistance force is desirable so that the musculo-skeletal system of crew members can be loaded to provide the required counter measures.
The same considerations apply in connection with many other types of equipment that make use of resistive force.
The present invention is directed to a resistance mechanism which is characterized by light weight, portability, and versatility, such that individual resistance packs may be used alone or in combination to create a relatively constant or varying resistance force throughout its range of motion. It is the principal goal of the invention to provide a resistance mechanism which has these characteristics and which can be used in a wide variety of applications where a resistance force is required.
More particularly, it is an important object of the invention to provide a resistance mechanism in which the resistive force is obtained by connecting resistance packs together in a series arrangement. This feature allows the cord or other actuator element to be extended a considerable distance without the resistance force varying unduly throughout the operating range of the mechanism. Another object of the invention is to provide a resistance mechanism which achieves a substantially constant force with increased extension through the use of a pulley having a progressively increasing diameter around which the cord is wrapped in a spiral configuration. The cord is received in a spiral groove formed in the surface of the pulley, and the pulley diameter increases progressively from bottom to top. Thus, as the cord is extended, it applies a force to the pulley at an increasingly large diameter part of the pulley. As the resistance elements are increasingly deformed with increasing extension of the cord, their resistance increases somewhat. This increased resistance is essentially canceled by the increased moment arm that results from the rope acting on a larger diameter portion of the pulley as the rope is extended. Depending upon the application, the diameter of the pulley may vary, allowing the moment arm to also vary.
A further object to the invention is to provide a resistance mechanism in which the resistive force can be easily pre-set to any desired level throughout a large range of resistance.
An additional object of the invention is to provide a resistance mechanism which is constructed using resistance packs that are specially arranged to include two resistance elements each, with the arms of each elastomeric element formed as loops and looped around walls on the base of the pack. This construction is efficient and effective, inexpensive to manufacture, reliable in operation and compact.
In accordance with the invention, a resistance mechanism is constructed by connecting a selected number of resistance packs together in a series arrangement. Each resistance pack has a rim and a central hub connected to the rim or adjacent to the rim by elastomeric spokes or arms which stretch to resist turning of the rim relative to the hub. The resistance packs are arranged in pairs, which the rims in each pair connected with one another. The pairs of resistance packs are arranged in a stack centered on a shaft. Splined sleeves are mounted on the shaft and mate with splines on the hubs of the resistance packs. The hubs of each pack have spline connections with the hubs of resistance packs in adjacent pairs. However, the hubs of the packs in each pair are not connected and can turn relative to one another.
This series arrangement of the resistance packs is an important feature of the invention. When a force is applied to rotate the hub of one resistance pack, it is transmitted through the spokes to the rim, then to the rim of the other pack in the same pair, through its spokes to the hub, and through the spline connection to the hub of the pack in the adjacent pair. The force is transmitted in series in this way through all of the resistance packs, resulting in a relatively small and substantially equal deformation of the spokes in each pack. Consequently, as the actuator element is increasingly displaced, the spokes of all of the packs share the deformation, and the entire range of movement of the actuator is accommodated without any of the spokes reaching or approaching its deformation limit.
The rim or hub of the resistance pack on one end of the stack is held stationary. A spiral pulley having an increasing diameter from one end to the other may be secured to the rim or hub of the resistance pack on the opposite end of the stack. The actuator may take the form of a cord extending around the pulley in a spiral groove. This construction results in the cord acting against an increasingly larger diameter portion of the pulley as it is extended, thus counteracting the slightly increasing force that results from increasing deformation of the spokes as the cord is extended.
The resistance mechanism can be equipped with a preload mechanism which includes a gear secured to the resistance pack on the end of the stack opposite the pulley. A smaller gear operated by a hand crank can be turned to rotate the larger gear and thus apply an initial deformation to the stack which sets a preloaded resistance. A pawl mechanism acting on the gear system holds the gears in place in the preloaded setting. An indicator acting in cooperation with a force scale may provide a visual indication of the preload force.
An alternative construction of the resistance pack provides a single base which includes two resistance elements, one each on opposite sides of the base, taking the form of spiders each having a central hub and outwardly extending elastomeric spokes or arms that are looped around walls formed near the periphery of the base. This avoids the need to glue or otherwise physically fix the outer ends of the arms to the rim, and thus avoids the potential of detachment of the arms from the rim. This construction is also inexpensive and versatile in that a reduced number of parts and manufacturing steps are required, and resistance elements of different configurations can be used interchangeably on a single base.